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Water pressure too high after using hot water

01-04-2008, 10:07 AM

My house is about 8 years old. All original plumbing and 50gal natural gas hot water heater.
About 3 months ago, one morning after taking a shower, the whole house filter I have near the meter in my basement burst.
I had a plumber come out to replace the broken filter system with a new one. He said while he was there, he noticed the pressure was a bit on the high side (70ish) and backed it down to 50 using the PRV.

Since that day we experience very high pressure after running the hot water (shower, dishwasher, clothes washer, etc). The way we noticed is that now after using the hot water, our kitchen sink and our shower head would drip until we opened a faucet somewhere to relieve the pressure for about 10 seconds. In the 7 years of being in the house prior to this day, we never had a problem with the pressure.

Last night I bought a pressure gauge and ran a few tests:
I ran only cold water for about 5 minutes. Shut everything off and checked the pressure. It held steady at about 45psi.
I ran only HOT water for about 5 minutes. Shut everything off and checked the pressure. It started out at 45psi and about 10 minutes later was over 160psi!

I do NOT have an expansion tank near my water heater (or anywhere, for that matter).

It seems that adding an expansion tank would solve the problem. Does that seem right?

And if so, can anyone explain why all of a sudden we have this problem? Why did we not have this problem for the prior 7 years?

@ 160 psi, the T&P relief should have kicked in. I would change that out as well as install the expansion tank. If you have the check valve on the cold water side, make sure the tank is installed on the proper side.

I do have a relief valve on the water heater, yet it never lets any water out.

Is it possible that it is stuck? I'm afraid to manually test it for fear that it will not shut.

If I replace this water heater with a tankless unit, would I still need to have an expansion tank on the line?

Thanks!

once again, is it only the hot pressure that goes up or both the hot and cold?

the relief valve is bad. they are set for 125-150 psi.

you really don't want to swap to a tankless. but you can read all about that on other threads.
a tankless is less prone to thermal expansion as it only operates on demand.

your issue is either a check valve, regulator or real high city pressure before the regulator. what is your pressure before the regulaotr and after the regulator. when it goes to 160 is that both hot and cold

Comment

once again, is it only the hot pressure that goes up or both the hot and cold?

the relief valve is bad. they are set for 125-150 psi.

you really don't want to swap to a tankless. but you can read all about that on other threads.
a tankless is less prone to thermal expansion as it only operates on demand.

your issue is either a check valve, regulator or real high city pressure before the regulator. what is your pressure before the regulaotr and after the regulator. when it goes to 160 is that both hot and cold

The only way I've tested the pressure is on a sink that has a single temp control turned all the way to the cold side.

The pressure readings, then I guess are only on the cold side. However, the pressure readings I got were dictated by the use of either hot or cold on another faucet.

How easy/hard is it to change out the relief valve on the water heater?
I'm thinking I need to go buy an expansion tank, and while I'm there, get a new relief valve.

Why do I not want to swap to a tankless? (Besides the obvious high initial cost)

The only way I've tested the pressure is on a sink that has a single temp control turned all the way to the cold side.

The pressure readings, then I guess are only on the cold side. However, the pressure readings I got were dictated by the use of either hot or cold on another faucet.

How easy/hard is it to change out the relief valve on the water heater?

easy to change, but it needs to be piped to an approved location.
I'm thinking I need to go buy an expansion tank, and while I'm there, get a new relief valve.

good idea. but why the high pressure all of a sudden. you need to check the pre regulator pressure too. it could be a bad pressure regulator.

Why do I not want to swap to a tankless? (Besides the obvious high initial cost)

Thanks again!

high cost, no return on your savings, high required maintenance, low gpm. if the tank has worked in the past, just replace the tank heater. why spend $2500-4500 on something that has no real benefit in your application.

read some old threads on our tankless debate. lots of exchange of thoughts.
rick.

Comment

good idea. but why the high pressure all of a sudden. you need to check the pre regulator pressure too. it could be a bad pressure regulator.

That's what I'd like to know!
I suppose you're talking about the "PRV" right?

If it is a PRV issue, wouldn't the pressure reading ALWAYS be too high, not be dependent on if hot or cold water was just in use? Plus, the Water Company guy said there is no way 160psi is coming in my house. He said if it was, then he'd be getting calls from people all over my block.

Could the T&P valve on the WH just recently have stopped working? If it were working correctly, would it ever just relieve pressure without letting out water at the same time?

That's what I'd like to know!
I suppose you're talking about the "PRV" right?

If it is a PRV issue, wouldn't the pressure reading ALWAYS be too high, not be dependent on if hot or cold water was just in use? Plus, the Water Company guy said there is no way 160psi is coming in my house. He said if it was, then he'd be getting calls from people all over my block. still would like to know the high pressure side of the regulator. the city street pressure. please post for the 3rd. time

regulators typically have a thermal expansion bypass.

Could the T&P valve on the WH just recently have stopped working? If it were working correctly, would it ever just relieve pressure without letting out water at the same time?

no if it relieves it leaks.

Thanks!

there is always going to be thermal expansion. but it will typically go back into the city main. unless you have a check valve or 150# plus pressure before the regulator.

need to know the pressure. a regulator doesn't last forever. also watch the gage on the cold side with the heater not heating. it probably is not holding at 45.

you need to find out the reason the pressure is going to 160. either a check valve, or bad regulator, or high city main pressure.

not too many other things can cause this.

need that high pre regulator pressure. this is the key to my next answer.

Comment

I honestly don't know the answer why after 7 years, this problem is happening. Could the the new house filter have anything to do with it? That and the PRV(he did reduce the pressure?) was touched. Nothing else changed. Any of these 2 possible?

Why is this just now an issue? How come in 7 years we never had an issue with this expansion/pressure build? There is nothing different in the system that I know of.

Thanks!

there is, that's why all the questions. something has changed. i'm trying to figure out what. how long has that backflow preventer been installed. that's when your issues started. or you fixed all the dripping/ running fixtures in the system

rick.

phoebe it is

Comment

The reason we had the plumber come out in the first place is because the existing whole whose filter burst. The container that screws into the unit that holds the filter cartridge broke at the threads.

I'm tempted to think that was a result of the pressure being too high. And it did burst about 10 minutes after I got out of the hot shower. But why that day? Why not any day before that? That filter had been on our system for years.

So, after that happened, we called a plumber who replaced the filter unit with a completely different brand. He also installed one (maybe two) new shut off valves to "isolate" the water filter. He said he adjusted the PRV down. The backflow preventer has been on the system since the house was built 7 years ago.

So as much as I am tempted to think it is something the plumber did that is causing the new pressure issue....I'm thinking the pressure issue started just before he got there.